To date, valves based on gasoline injection valves have been frequently used in gas engines. Since natural gas used up to this point contains a small fraction of oil due to oil-sealed compressors, these valves have a sufficiently long functional life, since very small amounts of oil are already sufficient for reliable operation.
However, in future applications, one must be prepared for the fact that gas engines will increasingly be driven by gases that are compressed in an oil-free manner and are, at the same time, almost completely dried with the aid of, in particular, a low-temperature dryer. Tests with such oil-free, dry gases in engines having gasoline injection valves according to the related art have shown that this reduces the functional life of the valves from several thousand hours at present, to a few hours. In particular, it was determined that valve needles already seize up after 10 hours to 100 hours of operating time or testing time, using dry nitrogen. This problem also relates to further dry gases, such as hydrogen.
On the other hand, carbon-containing layers in the form of so-called DLC layers (diamond-like carbon) or iC-WC layers are also used to provide wear protection to components subjected to high tribological loading, e.g. components of injection systems or injection valves. However, even these fail during use in an absolutely dry environment. In the case of injectors, this may easily be seen in a model wear test (vibrational wear), in a time-lapse motion camera. In this context, a test piece is loaded by an oscillating ball made of steel (100Cr6), a measure of the durability of the test piece provided with such a coating being the time to failure of the coating on the test piece.
In addition, it is known that the coefficient of friction in a dry environment may be reduced by increasing the level of hydrogen in diamond-like carbon layers or DLC layers. Thus, in A. Erdemir et al., “Effect of source gas and deposition method on friction and wear performance of diamond-like carbon films”, Surf. and Coatings Technology, 94-95, (1997), pages 525 ff., it is said that diamond-like carbon layers have a coefficient of friction of 0.02 in a dry environment, as long as they have an increased level of hydrogen. In this case, such an increase in the level of hydrogen is achieved by using methane or a methane/hydrogen mixture in place of acetylene during the deposition of the diamond-like carbon layer.
Furthermore, PCT International Publication No. WO 97/04142 describes a coating and a method for producing it, the coating also having a low coefficient of friction under dry conditions, but only having a low wear resistance. The coating produced there is made of molybdenum silicide and is applied to the surface to be coated, using a sputtering method.
An object of the present invention is to provide a tribologically loaded component, which is provided with a coating so that the component may also be used in an internal combustion engine or a gas engine driven by a dry, in particular oil-free gas as a fuel. In particular, the tribologically loaded component shall be provided with a coating, which has both a low coefficient of friction and a high wear resistance.